Homogeneous preparations of 3'-phosphoglycolate-terminated oligodeoxynucleotides from bleomycin-treated DNA as verified by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Single- and double-strand breaks bearing 3'-phosphoglycolate termini are among the most frequent lesions formed in DNA by ionizing radiation and other oxidative mutagens. In order to obtain homogeneous preparations of defined 3'-phosphoglycolate substrates for repair studies, 5'-(32)P-end-labeled partial duplex DNAs were treated with bleomycin, and individual cleavage products were isolated from polyacrylamide gels. The fragments were then treated with alkaline phosphatase and further purified by reverse-phase HPLC. Electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry of the purified oligomers produced molecular ions of the expected masses, with no detectable contaminants. Gas-phase sequencing by tandem mass spectrometry of these single species yielded the expected sequence ions and confirmed the presence of phosphoglycolate on the 3'-terminal fragments only. The fragments could be relabeled with polynucleotide kinase to yield highly purified, high-specific-activity substrates for repair studies.